1. Field of the Invention
This invention relates to pressure sensor apparatus, and more particularly to packaging of a pressure sensor cell.
2. Description of the Prior Art
In U.S. Pat. No. 3,808,480, Samuel Andrew Johnston discloses a capacity pressure transducer which has a pair of pressure responsive diaphragms as one set of capacitor plates which move with respect to respective fixed capacitor plates to constitute variable capacitors. In this construction, a substrate carries the fixed plates and, insulated from the fixed plates, a pair of cup-shaped pressure deformable diaphragm plates. The capacitance is connected in an electrical circuit which converts the varying capacitance to a correspondingly varying electrical signal. If the variable capacitor is part of an oscillator, the changes in pressure cause corresponding changes in the operating frequency of the oscillator and the variable frequency output signal can be processed by a discriminator or the like to obtain an analog output signal or by a counter to obtain a digital output signal, as disclosed in U.S. Pat. Nos. 3,295,360 and 3,595,084.
The variable capacitance disclosed by Johnston is mounted in a sealed chamber which has a pressure port for communication with a source of pressure which is to be monitored. Inasmuch as the pressure sensor cell disclosed by Johnston and the circuits disclosed by Johnston and in U.S. Pat. Nos. 3,295,360 and 3,595,084 may be utilized in practicing the present invention, these patents are fully incorporated herein by this reference.
Inasmuch as pressure sensors are finding use in a wide variety of applications, it is necessary, for certain applications, to provide an environmentally isolated, shock absorbing package for a pressure sensor cell, while at the same time providing for simultaneous pressure and/or vacuum detection on both diaphragms.